Since phototherapy was introduced in the United States in the 1960's it has proven effective in reducing serum bilirubin levels and decreasing the need for exchange transfusion in newborn infants with hyperbilirubinermia. Currently it is accepetd treatment in many hospitals. Despite general acceptance, many questions remain regarding safety of phototherapy. This study is designed to answer the most important of these questions; namely, is phototherapy effective in preventing brain injury from hyperbilirubinemia, when employed to lower serum billirubin levels? Answers to an additional question may be available: Is phototherapy as effective as exchange transfusion at predetermined serum billirubin levels for preventing brain damage from neonatal hyperbilirubinemia?